linux-kernel - Re: [PATCH v3 1/1] PCI: of: Relax max-link-speed check to support PCIe Gen5/Gen6

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Message-ID: <eba1f55e-3396-052c-0d77-09bf8b8c8216@linux.intel.com>
Date: Wed, 5 Nov 2025 10:45:04 +0200 (EET)
From: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
To: Hans Zhang <18255117159@....com>
cc: bhelgaas@...gle.com, helgaas@...nel.org, linux-pci@...r.kernel.org, 
    LKML <linux-kernel@...r.kernel.org>, 
    Manivannan Sadhasivam <mani@...nel.org>
Subject: Re: [PATCH v3 1/1] PCI: of: Relax max-link-speed check to support
 PCIe Gen5/Gen6

On Wed, 5 Nov 2025, Ilpo Järvinen wrote:

> On Sun, 2 Nov 2025, Hans Zhang wrote:
> 
> > The existing code restricted `max-link-speed` to values 1~4 (Gen1~Gen4),
> > but current SOCs using Synopsys/Cadence IP may require Gen5/Gen6 support.
> > 
> > While DT binding validation already checks this property, the code-level
> > validation in `of_pci_get_max_link_speed` also needs to be updated to allow
> > values up to 6, ensuring compatibility with newer PCIe generations.
> > 
> > Signed-off-by: Hans Zhang <18255117159@....com>
> > Reviewed-by: Manivannan Sadhasivam <mani@...nel.org>
> > ---
> > Changes for v3:
> > - Modify the commit message.
> > - Add Reviewed-by tag.
> > 
> > Changes for v2:
> > https://patchwork.kernel.org/project/linux-pci/cover/20250529021026.475861-1-18255117159@163.com/
> > - The following files have been deleted:
> >   Documentation/devicetree/bindings/pci/pci.txt
> > 
> >   Update to this file again:
> >   dtschema/schemas/pci/pci-bus-common.yaml
> > ---
> >  drivers/pci/of.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/drivers/pci/of.c b/drivers/pci/of.c
> > index 3579265f1198..53928e4b3780 100644
> > --- a/drivers/pci/of.c
> > +++ b/drivers/pci/of.c
> > @@ -890,7 +890,7 @@ int of_pci_get_max_link_speed(struct device_node *node)
> >  	u32 max_link_speed;
> >  
> >  	if (of_property_read_u32(node, "max-link-speed", &max_link_speed) ||
> > -	    max_link_speed == 0 || max_link_speed > 4)
> > +	    max_link_speed == 0 || max_link_speed > 6)
> >  		return -EINVAL;
> >  
> >  	return max_link_speed;
> > 
> 
> Hi,
> 
> IMO, using a literal here is somewhat annoying as it's hard to find this 
> spot when adding support to the next PCIe Link Speed. It would be nice if 
> it could get updated at the same while the generic support for a new Link 
> Speed is added.
> 
> Perhaps include/linux/pci.h should have something along the lines of:
>
> static inline int pcie_max_supported_link_speed()
> {
> 	return PCI_EXP_LNKCAP_SLS_64_0GB - PCI_EXP_LNKCAP_SLS_2_5GB + 1;
> }

...Or maybe put it just to drivers/pci/pci.h instead.

> Then replace that 6 with pcie_max_supported_link_speed().
> 
> So when the next speed get's added, somebody grepping for 
> PCI_EXP_LNKCAP_SLS_64_0GB will find pcie_max_supported_link_speed() has 
> to be changed and the change will propagate also to of.c.
> 
> 

-- 
 i.